Induction of Defense-Related Responses in Cf9 Tomato Cells by the AVR9 Elicitor Peptide of Cladosporium fulvum Is Developmentally Regulated

The AVR9 elicitor from the fungal pathogen Cladosporium fulvum induces defense-related responses, including cell death, specifically in tomato (Lycopersicon esculentum Mill.) plants that carry the Cf-9 resistance gene. To study biochemical mechanisms of resistance in detail, suspension cultures of tomato cells that carry the Cf-9 resistance gene were initiated. Treatment of cells with various elicitors, except AVR9, induced an oxidative burst, ion fluxes, and expression of defense-related genes. Agrobacterium tumefaciens-mediated transformation of Cf9 tomato leaf discs with Avr9-containing constructs resulted efficiently in transgenic callus formation. Although transgenic callus tissue showed normal regeneration capacity, transgenic plants expressing both the Cf-9 and the Avr9 genes were never obtained. Transgenic F₁ seedlings that were generated from crosses between tomato plants expressing the Avr9 gene and wild-type Cf9 plants died within a few weeks. However, callus cultures that were initiated on cotyledons from these seedlings could be maintained for at least 3 months and developed similarly to callus cultures that contained only the Cf-9 or the Avr9 gene. It is concluded, therefore, that induction of defense responses in Cf9 tomato cells by the AVR9 elicitor is developmentally regulated and is absent in callus tissue and cell-suspension cultures, which consists of undifferentiated cells. These results are significant for the use of suspension-cultured cells to investigate signal transduction cascades.     

Characterization of Laccases and Peroxidases from Wood-Rotting Fungi (Family Coprinaceae)

Panaeolus sphinctrinus, Panaeolus papilionaceus, and Coprinus friesii are described as producers of ligninolytic enzymes. P. papilionaceus and P. sphinctrinus both produced a laccase. In addition, P. sphinctrinus produced a manganese peroxidase. C. friesii secreted a laccase and two peroxidases similar to the peroxidase of Coprinus cinereus. The purified laccases and peroxidases were characterized by broad substrate specificities, significant enzyme activities at alkaline pH values, and remarkably high pH optima. The two peroxidases of C. friesii remained active at pH 7.0 and 60°C for up to 60 min of incubation. The peroxidases were inhibited by sodium azide and ethylene glycol-bis(β-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), whereas the laccases were inhibited by sodium azide and N,N-diethyldithiocarbamic acid. As determined by native polyacrylamide gel electrophoresis and isoelectric focusing, all three fungi produced laccase isoenzymes.     

Titin Extensibility In Situ: Entropic Elasticity of Permanently Folded and Permanently Unfolded Molecular Segments

Abstract. Titin (also known as connectin) is a giant protein that spans half of the striated muscle sarcomere. In the I-band titin extends as the sarcomere is stretched, developing what is known as passive force. The I-band region of titin contains tandem Ig segments (consisting of serially linked immunoglobulin-like domains) with the unique PEVK segment in between (Labeit, S., and B. Kolmerer. 1995. Science. 270:293–296). Although the tandem Ig and PEVK segments have been proposed to behave as stiff and compliant springs, respectively, precise experimental testing of the hypothesis is still needed. Here, sequence-specific antibodies were used to mark the ends of the tandem Ig and PEVK segments. By following the extension of the segments as a function of sarcomere length (SL), their respective contributions to titin's elastic behavior were established. In slack sarcomeres (~2.0 μm) the tandem Ig and PEVK segments were contracted. Upon stretching sarcomeres from ~2.0 to 2.7 μm, the “contracted” tandem Ig segments straightened while their individual Ig domains remained folded. When sarcomeres were stretched beyond ~2.7 μm, the tandem Ig segments did not further extend, instead PEVK extension was now dominant. Modeling tandem Ig and PEVK segments as entropic springs with different bending rigidities (Kellermayer, M., S. Smith, H. Granzier, and C. Bustamante. 1997. Science. 276:1112–1116) indicated that in the physiological SL range (a) the Ig-like domains of the tandem Ig segments remain folded and (b) the PEVK segment behaves as a permanently unfolded polypeptide. Our model provides a molecular basis for the sequential extension of titin's different segments. Initially, the tandem Ig segments extend at low forces due to their high bending rigidity. Subsequently, extension of the PEVK segment occurs only upon reaching sufficiently high external forces due to its low bending rigidity. The serial linking of tandem Ig and PEVK segments with different bending rigidities provides a unique passive force–SL relation that is not achievable with a single elastic segment.     

Isozymes,Speciation and Evolution in the Polyploid Complex Cochlearia L. (Brassicaceae)

Within the genus Cochlearia L. sect. Cochlearia three isozyme systems (aspartate aminotransferase, leucine aminopeptidase and phosphoglucomutase) have been analysed at the populational level for eleven species with different ploidy levels. Nine loci complexes were resolved with a total of 33 alleles from 89 populations. In general, polyploids displayed higher numbers of alleles per species and per population. A notable exception is diploid C. pyrenaica with as many alleles as some polyploids. Data support: (1) the origin of tetraploid C. officinalis from C. pyrenaica s.l., particularly from C. aestuaria; (2) the allopolyploid origin of octoploid C. anglica from C. officinalis; (3) the allopolyploid origin of hexaploid inland taxa C. polonica, C. tatrae and C. bavarica via hybridization between C. pyrenaica and C. officinalis; (4) a putative allopolyploid origin of hexaploid coastal species C. danica by hybridization between C. pyrenaica s.l. and C. officinalis accompanied by a shift in chromosome complement. A scenario summarizing our present understanding of the evolution within Cochlearia sect. Cochlearia is presented.     

Assessment of Grey Heron predation on fish communities: the case of the largest European colony

The fish predation rate by Grey Heron Ardea cinerea was studied during two breeding seasons (1987–88) in the largest European colony at the Lake of Grand-Lieu (Loire-Atlantique, France). The herons' diet was compared to the available fish population of its main feeding area, the marsh of Bourgneuf (16000 ha) which is composed of former salt pans and meadows drained by a dense network of shallow ditches. This study is the first attempt to assess the predation exerted by an ardeid colony on a fish community over such an extensive natural environment. It also provides the first data about the abundance and the structure of fish communities in shallow coastal dyked marshes. For this purpose, two different sampling methods were used according to the water's salinity. In fresh waters, electrofishing was used as the removal method, and density estimates were calculated with Carle & Strub estimator (1978). Fish were caught in randomly selected stations (sections of ditches enclosed by two 5 mm mesh nets). In brackish waters, pools and ditches were drained. The distribution of the herons at the feeding areas was determined by direct observations, by counting flights from the colony, and by radio-tracking. The diet was investigated by observing adult herons on the foraging areas, and by analyzing the prey regurgitations of the young at the nests. The global food consumption was assessed from Marion (1988), according to the birds' activity determined during 5 years of radio-tracking. Altogether, at least 39 species of fish were available in the herons' feeding area (during the reference period, 87–88) and the mean fish biomass was 270 kg per ha of open water, or 30 kg per ha of marsh (open water = 11.2% of the marsh area). The fish community was dominated by eel Anguilla anguilla (145 kg ha^–1, 50,8% of the total biomass), and catfish Ictalurus melas (40 kg ha^–1, 14%). Except for small and inaccessible species (living in the deepest parts of the marsh), heron diet was very similar to fish species composition of the community occurring in the marsh. The catfish was the species captured most frequently by the heron (45% of the mass), the eel was second with 28% of the mass. The catfish was probably over represented in the diet considering that they are caught in catfish-dumps created by professional fishermen at Grand-Lieu lake, in order to reduce the density of this undesirable species. Inversely, small species such as Gasterosteus aculeatus were not found in the diet whereas they are very numerous in the marsh. On average herons of Grand-Lieu colony catch 1.92 kg of fish per ha of marsh (6% of the fish standing crops in the marsh) during the breeding season, the main predation period.